This invention relates to antennas, phased array antennas, and specifically to a wafer-scale heterogeneous layered active electronically scanned array (ESA) with a low-loss, integrated waveguide feed.
Electronically scanned arrays or phased array antennas offer significant system level performance enhancements for advanced communications, data link, radar, and SATCOM systems. The ability to rapidly scan the radiation pattern of the ESA allows the realization of multi-mode operation, LPI/LPD (low probability of intercept and detection), and A/J (antijam) capabilities. One of the major challenges in ESA design is to provide cost effective antenna array phase shifting methods and techniques along with dual-band operation of the ESA.
It is well known within the art that the operation of a phased array is approximated to the first order as the product of the array factor and the radiation element pattern as shown in Equation 1 for a linear array.
                                          E            A                    ⁡                      (            θ            )                          ≡                                                                              E                  p                                ⁡                                  (                                      θ                    ,                    ϕ                                    )                                            ︸                                      Radiation                              Element                Pattern                                              ⁢                                                                      [                                                            exp                      ⁡                                              (                                                                              -                            j                                                    ⁢                                                                                    2                              ⁢                              π                              ⁢                                                                                                                          ⁢                                                              r                                o                                                                                      λ                                                                          )                                                                                    r                      o                                                        ]                                ︸                                            Isotropic                                  Element                  Pattern                                                      ·                                                  ⁢                                                  ⁢                                                                                ∑                    N                                    ⁢                                                            A                      n                                        ⁢                                          exp                      ⁡                                              [                                                                              -                            j                                                    ⁢                                                                                    2                              ⁢                              π                                                        λ                                                    ⁢                          n                          ⁢                                                                                                          ⁢                          Δ                          ⁢                                                                                                          ⁢                                                      x                            ⁡                                                          (                                                                                                sin                                  ⁢                                                                                                                                          ⁢                                  θ                                                                -                                                                  sin                                  ⁢                                                                                                                                          ⁢                                                                      θ                                    o                                                                                                                              )                                                                                                      ]                                                                                            ︸                                            Array                ⁢                                                                  ⁢                Factor                                                                        Equation        ⁢                                  ⁢        1            
Standard spherical coordinates are used in Equation 1 and θ is the scan angle referenced to bore sight of the array. Introducing phase shift at all radiating elements within the array changes the argument of the array factor exponential term in Equation 1, which in turns steers the main beam from its nominal position. Phase shifters are RF devices or circuits that provide the required variation in electrical phase. Array element spacing is related to the operating wavelength and it sets the scan performance of the array. All radiating element patterns are assumed to be identical for the ideal case where mutual coupling between elements does not exist. The array factor describes the performance of an array of isotropic radiators arranged in a prescribed two-dimensional rectangular grid.
Wafer scale integration is a system known in the art for building very large integrated circuit networks that use an entire silicon wafer to produce a circuit function. The large size and reduced packaging requirements needed with wafer scale integration makes possible reduced costs and increased performance for some applications.
Wafer scale integration has been proposed for fabricating an active antenna array. “Wafer-Scale Integration Brings Low Cost and a Small Footprint to Active Antenna Arrays,” by Fred Mohamadi, RF Design, February 2005 discloses a 256-element steerable antenna array on an eight-inch wafer. The wafer scale array module disclosed provides transmit and receive functions and a steerable 16 by 16 element antenna on the eight-inch wafer. The wafer scale integration concept disclosed comprises a radiating element layer, a device layer and a signal distribution layer. The RF interconnection layer uses coplanar waveguide (CPW) or shield microstrip transmission lines. One of the problems with the coplanar waveguides and microstrip feed implementations at the subarray level are the large losses.
What is needed is a low-loss active electronically scanned antenna (ESA) feed that is compatible with a heterogeneous wafer-scale stacked active transmit/receive (T/R) subarray modules. Furthermore what is needed is a second layer low-loss combining scheme to tile the subarrays into arbitrarily sized non-conformal apertures.